Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 19 4 2026 03 04 1776 1776 EN Behzad Nourozi Research Center of Health and Environment, School of Health, Guilan University of Medical Sciences, Rasht, Iran Shahyad Azariamidian Research Center of Health and Environment, School of Health, Guilan University of Medical Sciences, Rasht, Iran, Department of Medical Parasitology, Mycology and Entomology, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran Farzad Majidi-Shilsar Department of Plant Protection, Rice Research Institute, Rasht, Iran Mohammad Noori-Sepehr Research Center for Health, Safety and Environment, Department of Environmental Health, School of Health, Alborz University of Medical Sciences, Karaj, Iran Mohammad Naimi-Joubani Research Center of Health and Environment, School of Health, Guilan University of Medical Sciences, Rasht, Iran, Research Center for Health, Safety and Environment, Department of Environmental Health, School of Health, Alborz University of Medical Sciences, Karaj, Iran 2024 10 22 2026 02 23 Background: The German cockroach, Blattella germanica (Blattaria: Ectobiidae), is a worldwide urban pest. Due to limitations of conventional insecticides, alternative controls are needed. Entomopathogenic fungi-based biopesti­cides offer a promising solution. This study evaluated the pathogenicity of the indigenous Beauveria bassiana Rasht strain (Mcb18) against the German cockroach. Methods: A laboratory colony of B. germanica was maintained under controlled conditions. The toxicity of four spore concentrations (1.5×10², 1.5×10⁴, 1.5×10⁶, 1.5×10⁸ conidia/ml) of B. bassiana was evaluated against adult cockroaches using the direct immersion bioassay. Daily mortality was recorded for 21 days using three replicates of 20 cockroaches each (n=60 per concentration). The lethal concentration (LC50 and LC90) values were estimated us­ing probit analysis. Results: Beauveria bassiana caused dose-dependent mortality. The highest cumulative mortality (100%) was ob­served at 1.5×10⁸ conidia/ml, while the lowest (15.79%) occurred at 1.5×10² conidia/ml. The LC50 and LC90 were estimated as 4.23×10³ conidia/ml and 1.59×10⁶ conidia/ml, respectively. The LT50 decreased with increasing concen­tration, reaching 8.475 days at 1.5×10⁸ conidia/ml. Conidiation on cadavers increased with concentration but re­mained lower than mor­tality, indicating that death often occurred before external sporulation. One-way ANOVA revealed significant differ­ences in mortality rates (F=74.942, df=(3, 8), p<0.001). Post-hoc Tukey's HSD test showed that the two highest concen­trations (1.5×10⁶ and 1.5×10⁸ conidia/ml) were not significantly different from each oth­er (p>0.05), although both caused significantly higher mortality than lower concentrations (p<0.001). Conclusion: Experimental findings confirmed B. bassiana as an effective entomopathogen against B. germanica, caus­ing significant mortality through cuticular penetration and internal proliferation. https://jad.tums.ac.ir/index.php/jad/article/view/1776 https://jad.tums.ac.ir/index.php/jad/article/download/1776/714